The document discusses light and the electromagnetic spectrum. It explains that light is composed of vibrating electric and magnetic fields and is part of the electromagnetic spectrum, which includes gamma rays, x-rays, ultraviolet rays, visible light, infrared, microwaves, and radio waves. It also discusses the energy of light photons, the visible light spectrum, color, and how dispersion via a prism separates white light into a rainbow spectrum due to differences in wavelengths traveling at different speeds in a medium.

1. LIGHT

2. Why did the apple appear black when using the red
cellophane-covered flashlight?
What colors did you see when you used different color of
cellophane to flash light on the apple? Using the mango?

3. ELECTROMAGNETIC SPECTRUM
◦ LIGHT – composed of vibrating electric and magnetic fields coupled
with each other with a speed of 3.00 x 108 in vacuum. It is part of the
wide electromagnetic spectrum.

4. Types of electromagnetic waves according to
increasing wavelength (or decreasing frequency).
◦ Gamma rays – with highest frequency means most energetic, and the
most dangerous of all
◦ X-rays
◦ Ultraviolet (UV) rays
◦ Visible light
◦ Infrared
◦ Microwaves
◦ Radio waves – lowest frequency means least energetic, and the safest
:ALL OF THEM COMPRISES THE ELECTROMAGNETIC SPECTRUM:

5. ENERGY OF LIGHT
◦ Light is a form of energy.
◦ Each photon of light can be thought of as a small a particle carrying
energy.
◦ Amount of this energy E is proportional to the frequency of the
corresponding electromagnetic wave:
E = hf
where h is called Planck’s constant (6.626 x 10-34 J/hz).

6. ◦ Planck’s constant is named after German physicist Max Karl Enst Ludwig
Planck (1859-1947).
◦ Also he is the who first formulated the quantum theory.
Example: a photon of red light
red light (frequency) is 4.5 x 1014 Hz, carries an amount of energy of
about 3.0 x 1019J
◦ a photon with twice as much energy corresponds to a wave with twice the
frequency. This lies in the ultraviolet range of the electromagnetic spectrum.
◦ On the other hand, a photon of infrared light carries half of as much as energy
because it corresponds to a wave with half the frequency.

7. VISIBLE LIGHT
◦ the narrow band of the electromagnetic spectrum that can be
detected by the human eye.
◦ Red light has the lowest frequencies at 3.84 x 1014 and the longest
wavelength of the visible light.
◦ Violet on the other hand, has the highest frequencies at 7.69 x
1014 Hz and the shortest wavelength.

9. When you look directly at the sun, the light appears white (mixture of all
the wavelengths in the visible spectrum). The more intense found in the
middle of visible spectrum.
This was first realized by Newton during his years of studying the nature
of light.

10. COLOR
◦ most objects thaw we see is a mere reflectionof visible light
emitted by a light source (such as sun, light bulbs, and fireflies).
◦ As the light strikes to the object, it may either be reflected or
absorbed by the object.
◦ The relative amount of reflection, absorption, and transmission
typically differ for different wavelengths.
◦ Ex: ripe mango (it appears yellow because it reflects (yellow color)
and absorb most of the other colors)

11. COLOR
◦ Colors are subjective human physiological and psychological responses,
primarily to various frequency regions. (from about 384 THz through O,
Y, G, B, to violet at about 769 THz).
◦ Color is not a property of light, but a manifestation of electrochemical
sensing system – eyes, nerves, and brain.
◦ We should not say “blue light”, rather light that appears to be blue”.
◦ Color blindness people, they cannot compare some of the colors that
are visible to other people.

12. DISPERSION AND PRISM
◦ Light waves at different wavelengths travel at different speeds in a
given medium.
◦ Red light travels the fastest while violet travels the slowest. Because of
this, violet is bent more than red light when it passes from one medium
to another.
◦ When light passes from air to glass in a prism, violet bends most while
red bends the least. The rest are bent in between.
◦ This effect, in which light is separated into different colors because of
differences in wave speed is called DISPERSION.